Distinct patterns in alpine vegetation around dens of the Arctic fox

The arctic fox Alopex lagopus excavates its dens in gravely ridges and hillocks, and creates a local environment quite distinct from the surrounding tundra or heath landscape. In northern Sweden, the vegetation of 18 dens of the arctic fox was investigated, as well as reference areas off the dens but in geologically and topographically similar locations. The species composition showed considerable differences between den and reference areas, with grasses and forbs occurring more abundantly on the dens, and evergreen dwarf-shrubs occurring more in reference areas. The effect of the foxes' activities is thought to be either through mechanical soil disturbance, or through nutrient enrichment via scats, urine, and carcasses. This was expected to result in differences in plant traits with key functional roles in resource acquisition and regeneration, when comparing dens with reference areas. We hypothesised that the community mean of specific leaf area (SLA) would differ if nutrient enrichment was the more important effect, and that seed weight, inversely proportional to seed number per ramet and hence dispersal ability, would differ if soil disturbance was the more important effect. Specific leaf area showed a significant difference, indicating nutrient enrichment to be the most important effect of the arctic fox on the vegetation on its dens. Arctic foxes act as ecosystems engineers on a small scale, maintaining niches for relatively short-lived nutrient demanding species on their dens in spite of the dominance of long-lived ericaceous dwarf-shrubs in the landscape matrix. Thus, foxes contribute to the maintenance of species richness on the landscape level.